Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
DOI 10.1186/s12906-015-0718-0
RESEARCH ARTICLE
Open Access
Optimization protocol for the extraction of
6-gingerol and 6-shogaol from Zingiber officinale
var. rubrum Theilade and improving antioxidant
and anticancer activity using response surface
methodology
Ali Ghasemzadeh1*, Hawa Z.E. Jaafar1 and Asmah Rahmat2
Abstract
Background: Analysis and extraction of plant matrices are important processes for the development,
modernization, and quality control of herbal formulations. Response surface methodology is a collection of
statistical and mathematical techniques that are used to optimize the range of variables in various experimental
processes to reduce the number of experimental runs, cost , and time, compared to other methods.
Methods: Response surface methodology was applied for optimizing reflux extraction conditions for achieving
high 6-gingerol and 6-shogaol contents, and high antioxidant activity in Zingiber officinale var. rubrum Theilade . The
two-factor central composite design was employed to determine the effects of two independent variables, namely
extraction temperature (X1:50–80 °C) and time (X2:2–4 h), on the properties of the extracts. The 6-gingerol and
6-shogaol contents were measured using ultra-performance liquid chromatography. The antioxidant activity of
the rhizome extracts was determined by means of the 1,1-diphenyl-2-picrylhydrazyl assay. Anticancer activity of
optimized extracts against HeLa cancer cell lines was measured using MTT (3-(4,5-dimethylthiazol-2-yl)-2,
5-diphenyltetrazolium bromide) assay.
Results: Increasing the extraction temperature and time induced significant response of the variables. The
optimum extraction condition for all responses was at 76.9 °C for 3.4 h. Under the optimum condition, the
corresponding predicted response values for 6-gingerol, 6-shogaol, and the antioxidant activity were 2.89 mg/g
DW, 1.85 mg/g DW, and 84.3 %, respectively. 6-gingerol and 6-shogaol were extracted under optimized condition
to check the viability of the models. The values were 2.92 and 1.88 mg/g DW, and 84.0 % for 6-gingerol, 6-shogaol,
and the antioxidant activity respectively. The experimental values agreed with those predicted, thus indicating
suitability of the models employed and the success of RSM in optimizing the extraction condition. With optimizing
of reflux extraction anticancer activity of extracts against HeLa cancer cells enhanced about 16.8 %. The half inhibition concentration (IC50) value of optimized and unoptimized extract was found at concentration of 20.9 and
38.4 μg/mL respectively. Optimized extract showed more distinct anticancer activities against HeLa cancer cells in a
concentration of 40 μg/mL (P < 0.01) without toxicity to normal cells.
Conclusions: The results indicated that the pharmaceutical quality of ginger could be improved significantly by
optimizing of extraction process using response surface methodology.
Keywords: 6-Gingerol, 6-Shogaol, DPPH activity, Zingiber officinale var. rubrum Theilade, Response surface
methodology
* Correspondence: alighasemzadeh@upm.edu.my
1
Department of Crop Science, Faculty of Agriculture, Universiti Putra
Malaysia, 43400 Serdang, Selangor, Malaysia
Full list of author information is available at the end of the article
© 2015 Ghasemzadeh et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution
License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://
creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
Background
Herbs and natural products are precious sources of medicinal compounds and their benefits and importance
for healing have been well recognized since ancient
times. The characteristics and health effects of natural
bioactive compounds, especially from plant sources including spices, have been extensively investigated. Phytochemicals are important compounds found in medicinal
plants that are not essential for the normal functioning
of the human body, but are active and exert positive effects on health or in amelioration of diseases. Many phytochemicals have been identified though a great many
are yet to be identified [1]. According to a report by the
World Health Organization, 80 % of the population in
developing countries depends on traditional medicine
for their primary health care, and 85 % of traditional
medicine is derived from plant extracts [2]. In Malaysia,
herbs and spices are generally consumed raw and fresh
as vegetables (salad), especially by the Malay community.
Ginger (Zingiber officinale Roscoe) is one of the most
widely used spices in the world, especially in Malaysia
and locally was known as Halia. Owing to its universal
appeal, ginger has spread to most tropical and subtropical countries from China and India, where ginger cultivation has been prevalent, possibly since prehistoric
times [3]. In ancient times, ginger was highly valued for
its medicinal properties and it played an important role
in primary health care in ancient India and China. Ginger contains a variety of pungent and biologically active
compounds, primarily 6-gingerol, 6-shogaol, zingerone, phenolics, and flavonoids [4]. Between identified
components, 6-gingerol was reported as the most
abundant bioactive compound in ginger with various
pharmacological effects including antioxidant, analgesic, anti-inflammatory and antipyretic properties [5–8].
The result of recent studies showed that 6-shogaol with
lowest concentration in ginger represent more biologically
actives compared to 6-gingerol [9–11] Dugasani et al. [12]
reported 6-shogaol as a potent anti-inflammatory and
antioxidant compounds in ginger. Various methods for
the analysis of 6-gingerol and 6-shogaol in ginger extract
have been reported [13–15] but, among these, highperformance liquid chromatography (HPLC) is most
widely utilized. Extraction prior to component analysis is
the main step for the recovery and isolation of bioactive
phytochemicals from plant materials. Analysis and extraction of plant matrices are important processes for the
development, modernization, and quality control of herbal
formulations [13]. In general, the first step of complete
extraction is the selection of plant parts and careful preparation of plant extracts, and a thorough review of the
existing literature to learn about the most suitable protocols for a specific group of compounds or plant species.
Traditionally, the extraction of 6-gingerol and 6-shogaol
Page 2 of 10
compounds is accomplished by reflux or Soxhlet extraction
[16]. However, prolonged extraction at high temperature
may degrade the 6-gingerol and 6-shogaol compounds,
and involves high energy cost. Bhattarai et al. [17] recently
reported that in acidic media and under high extraction
temperature 6-gingerol can be degraded to 6-shogaol.
Generally, the widespread use of ginger as a spice, dietary
supplement, tea, cream, household remedy, as well as
an ingredient of various herbal formulations, requires
standardization of ginger formulations. A model for optimizing the most relevant operational parameters is required in order to achieve higher extraction yield. Response
surface methodology (RSM) is a collection of statistical and
mathematical technique that used to optimize the range of
variables in various experimental processes with reducing
the number of experimental runs, cost and time compared
to other methods. Zingiber officinale var. rubrum Theilade
is distributed mainly in Peninsular Malaysia, where it is
known locally as halia udang, halia merah and halia bara.
To the best of our knowledge, no other studies have been
undertaken to optimize extraction condition of 6-gingerol
and 6-shogaol from Z.officinale.var.rubrum Theilade. The
aim of this study was to optimize the conditions for the
extraction of a Malaysian ginger variety Zingiber officinale
var. rubrum Theilade namely Halia bara to achieve high
6-gingerol and 6-shogaol contents and high antioxidant
and anticancer capacity by using response surface methodology with a central composite design (CCD).
Methods
Plant materials
Z.officinale var. rubrum Theilade rhizomes were collected
from Bentong, Pahang, Malaysia. The samples were identified by herbarium of department of biology, faculty science, University Putra Malaysia. Rhizomes were washed
with pure water and were soaked in a Mancozeb solution
(0.3 %) for 30 min and were cut into 3–5 cm pieces containing 2 to 3 buds. After cutting, all pieces were planted
6 cm deep into the small pots filled with about 1 kg peat
moss. Rhizomes were grown in a glasshouse for two
weeks. Afterward, seedlings with 2 or 3 leaves were transplanted into polyethylene bags filled with a soilless mixture composed of burnt rice husk and coco peat (1:1).
Ginger is a semi-shade loving plant and needs shade for
growth and rhizome production. Then, the plants were
grown under glasshouse conditions at the glasshouse
complex of Universiti Putra Malaysia (UPM) where daily
irradiance was approximately 790 μmol/m2/s (light intensity in outside was 1150 μmol/m2/s). Relative humidity
was 70 ± 5 % and average temperature was 28 ± 1 °C. The
plants were harvested after nine month, with the leaves,
stems, and rhizomes separated. The rhizomes were shade
dried and were powdered using grinder. These powdered
materials were used for further analysis.
Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
Extraction
The optimization procedure for the extraction process
focusing on the extraction temperature (X1: 50–80 °C)
and extraction time (X2: 2–4 h) was devised based on
two factor central composite design, as summarized in
Table 1. Rhizomes of Z.officinale var. rubrum Theilade
were harvested and washed with water and shade dried.
Ten grams of dried rhizomes were extracted with absolute
ethanol (100 mL) for 2–4 h at 50- 80 °C using a reflux
apparatus (Table 1). The ginger extracts were filtered
through Whatman No.1 filter paper and kept at −20 °C
for future analysis.
Ultra High Performance Liquid Chromatography (UHPLC)
analysis
The UHPLC system (Agilent, Model 1200) with Agilent
C18 (4.6 × 250 mm, 5 μm) column was used for 6-gingerol
and 6-shogaol analysis. In this system two mobile phases
including: (A) water and (B) acetonitril (CAN) were used.
The column temperature, flow rate and injection volume
were adjusted at 48 °C, 1 mL/min, 20 μL. The UV absorbance was measured at 280 nm. To prepare the standard
solution 6-gingerol and 6-shogaol (0.0625, 0.125, 0.250,
0.500 and 1 mg/mL) were dissolved in HPLC grade methanol. The linear regression equation were calculated with
Y = aX ± b, where X was concentration of 6-gingerol and
6-shogaol and Y was the peak area of 6-gingerol and 6shogaol obtained from UHPLC. Identification of the compounds was achieved by comparison of retention times
with standards, UV spectra and UV absorbance ratios after
co-injection of samples and standards. System suitability
requirements: Perform at least five replicate injections of
6-gingerol and 6-shogaol. The requirements of the system
suitability parameters are : (1) Symmetry factor (As) is not
more than 1.5, (2) Percentage of relative standard deviation (RSD) of the retention time (tr) for 6-gingerol
and 6-shogaol standards is not more than 2.0 %.
Page 3 of 10
gently and incubated at 28 °C in a dark room for 40 min.
For the control, methanol was used as a blank. The
absorbance of the samples was read at 517 nm using
spectrophotometer. BHT (butylhydroxytoluene) and αtocopherol, were used as positive controls. The scavenging
activity was calculated using the following formula:
"
% inhibition ¼ ðabsorbance of control – absorbance of sampleÞ
#
absorbance of controlÞ 100
ð1Þ
Determination of anticancer activity
Retrieve the frozen cells from liquid nitrogen cell storage
tank and thaw the cells in cyrovials rapidly. Carefully
transfer the contents of the cyrovial to a centrifuge tube
and add 10 ml of pre-warmed media slowly to the cell
suspension. Spin down at 1000 rpm for 10 min and gently re-suspend pellet in 10 ml fresh media into culture
flask. Incubate in 37 °C humidified incubator supplemented with 5 % CO2. After 24 h, the old medium was
discard one day after seeding and adds 2-3 ml PBS to
cover all surface and discard. Add 1.5-2 ml trypsining
solution to cover the flask surface and leaved at room
temperature for 3 min until most of the cells detach.
Add 10 ml of complete medium. For MTT assay add
100 μl of cell into all the wells various concentrations of
optimized (76.9 °C and 3.4 h) and unoptimized (80 °C
and 4 h) extracts (10, 20, 40, 80 and 160 μg/mL) and incubate in 37 °C, 5 % CO2 incubator for 72 h. Prepare a
stock solution of 5 mg/ml MTT (3-(4,5-dimethylthiazol2-yl)-2,5-diphenyltetrazolium bromide) in Phosphate buffered saline (PBS) and add 20 μL of MTT reagent to cell
monolayer. Add 100 μl of DMSO (Dimethyl sulfoxide)
to each well and mix thoroughly by pipetting 10–20 times
to dissolved the blue formazan crystals. The absorbance of
samples was read at 570 nm using ELISA reader.
1,1-Diphenyl-2-picrylhydrazyl (DPPH) assay
The free radical scavenging activity of Z.officinale var.
rubrum Theilade extracts were determined according to
the Mensor et al. [18] with some modification. DPPH
was dissolved in methanol to give final concentration
of 2 mM. Following that, 1 mL of DPPH solution was
added to different concentration of curry leaf extracts
(20, 40, 60 80 and 100 mg/mL). The mixture was shaked
Table 1 Levels of independent variables for reflux extraction
condition based on CCD
Coded
Variable
−1
0
1
Axial (−α)
Axial (+α)
X1: extraction temperature
50
65
80
47.1
82.8
X2: extraction time
2
3
4
1.8
4.1
Experimental design
RSM software with central composite experimental
design (3-level, 2-factorial) was used to investigate and
validate extraction parameters affecting the extraction
yields of 6-gingerol (Y1), 6-shogaol (Y2) and antioxidant
activity (Y3) of Z.officinale var. rubrum Theilade rhizomes
extracts. In this study, 14 experiments were designed and
carried out in duplicate with different range of the independent variables, reflux temperature (X1: 50–80 °C) and
extraction time (X2: 2–4 h). In order to conduct the
experimental design and the statistical analysis the Design
Expert software (version 6.0) was used. Analysis of variance (ANOVA) and response surface analysis were used
to determine the statistical significance of the model. The
adequacy of the model was predicted through the
Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
ANOVA (P < 0.05) and regression analysis (R2). The relationship between the response and independent variables
was demonstrated using response surface plot. Initially, a
second-order polynomial model was set up to predict
the response variables. The equation is given below:
Y ¼ b0 þ b1 X 1 þ b2 X 2 þ b1 2 X 1 2 þ b2 2 X 2 2 þ b1 b2 X 1 X 2
Page 4 of 10
coefficient of determination (R2 = 0.97). The result indicated significant (P < 0.01) quadratic and linear effects of
the extraction temperature and time on 6-gingerol content (Y1). However, no interactive effect was observed for
the independent variables. The predicted model obtained
for Y1 is as follows:
ð2Þ
Y 1 ¼ 1:53 þ 0:51X 1 þ 0:25X 2 þ 0:31X 1 X 2 þ 0:27X 1 2
Where Y is the predicted dependent variable; b0 is a
constant that fixes the response at the central point of
the experiment; b1, b2, b21, b22, and b1b2 are the linear,
quadratic, and interaction coefficients, respectively. Graphical and numerical optimizations were performed to obtain
the optimum conditions and predicted values for the response variables based on the response optimizer.
ð3Þ
Results and Discussion
Effects of extraction conditions on 6-gingerol and
6-shogaol content
The reflux extraction was designed based on two-factor
CCD consisting of extraction temperature (X1: 50–80 °C)
and extraction time (X2: 2–4 h) at five levels each (Table 1).
The result of response surface methodology demonstrated
significant (P < 0.05) regression relationships between the
independent variables and response variables. A high content of 6-gingerol (2.74 mg/g DW) in the rhizome extract
was observed for treatment 3 (Table 2). The current
regression analysis also indicated that more than 80 % of
the variations could be explained by the models. Analysis
of variance for predicted extraction model of 6-gingerol
implies that the model is highly significant with a good
þ 0:009233X 2 2
Lack of fit test for the model describes the variation in
the data around the fitted model. If the model does not
fit the data well, the value of lack of fit will be significant
and then proceeding with investigation and optimization
of the fitted response surface is likely to give misleading
results [19]. In current study, the “Lack of Fit F -value”
of 4.12 implies that the Lack of Fit is not significant relative to the pure error (Table 3).
The response surface plot in Fig. 1a shows the relationship between the 6-gingerol content and the extraction
temperature, as well as time, illustrating that as the
temperature (47.1–82.8 °C) and time (1.8–4 h) increased,
the 6-gingerol content increased. Upon increasing the extraction time from 2 to 4 h at 80 °C, the 6-gingerol content
increased from 1.79 to 2.74 mg/g DW.
The result of previous study demonstrated that ß-hydroxy keto presence in gingerols structure is a sensitive
to high temperature and promotes dehydration of gingerols
at high temperature [17]. The present results are consistent
with observations by Bak et al. [16] who reported that when
ginger was extracted at room temperature, the 6-gingerol
Table 2 Experimental data and predicted content obtained for the dependent variables
Treatment
X1
X2
6-gingerol content
(mg/g DW)
Predicted content
of 6-gingerol
6-shogaol content
(mg/g DW)
Predicted content
of 6-shogaol
Antioxidant
activity %
Predicted content of
antioxidant activity %
1 (c)
65
3
1.49
1.52
1.25
1.20
68.0
71.0
2
50
4
1.08
1.21
0.90
1.02
62.5
65.0
3
80
4
2.74
2.80
1.59
1.63
89.0
83.8
4
80
2
1.79
1.73
1.20
1.12
78.0
78.3
5(c)
65
3
1.56
1.52
1.33
1.24
69.0
71.0
6(c)
65
3
1.42
1.52
1.21
1.20
68.0
71.0
7
50
2
1.38
1.33
1.04
1.08
66.0
60.8
8(c)
65
3
1.62
1.52
1.31
1.20
70.0
71.0
9
82.8
3
2.55
2.53
1.32
1.35
84.0
85.6
10
65
4.1
2.00
1.92
1.55
1.48
79.0
75.8
11
47.1
3
1.35
1.28
1.10
1.05
66.8
62.6
12(c)
65
3
1.52
1.52
1.28
1.20
73.0
71.0
13
65
1.8
1.11
1.19
0.82
0.97
66.0
68.0
14(c)
65
3
1.55
1.52
1.24
1.20
71.0
71.0
c central point
Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
Page 5 of 10
Table 3 Regression coefficients, R2, adjusted R2 and F-values for dependent variables
constant
linear
quadratic
Interaction
Responses
b0
b1
b2
b21
b22
b12
R2
R2 (adjusted)
Regression (F value)
Lack of fit (F value)
Y1
1.53
0.51
0.25
0.27
0.0092
0.31
0.97
0.95
45.91**
4.12 n.s
**
Y2
1.2
0.15
0.12
0.021
0.024
0.15
0.93
0.92
15.58
1.39 n.s
Y3
71.88
9.22
2.78
3.16
1.11
4.63
0.96
0.94
15.79**
1.24 n.s
n.s non significant
** = significant at p < 0.01
content tended to decrease as the drying temperature
increased up to 60 °C, whereas drying at 80 °C resulted in
an increase in the 6-gingerol yield. The origin of the
enhanced 6-gingerol content at 80 °C is not clear at this
moment.
Analysis of variance for predicted extraction model of
6-shogaol implies that the model is highly significant
with a good coefficient of determination (R2 = 0.93)
(Table 3). Significant (P <0.05) quadratic effects of the
extraction temperature and time on the 6-shogaol content (Y2) were observed. The predicted model obtained
for Y2 is as follows:
Y 2 ¼ 1:20 þ 0:15X 1 þ 0:12X 2 þ 0:15X 1 X 2
ð4Þ
The model F-value of 15.58 obtained for the 6-shogaol
content implies that the model is significant, with only a
0.07 % probability that such a large “model F-value” can
occur owing to noise. The “Lack of Fit F -value” of 1.39
implies that the Lack of Fit is not significant for the predicted model (Table 3). In the current study, treatment 3
yielded a high content of 6-shogaol in the ginger extract,
with a value of 1.59 mg/g DW. The predicted content of
6-shogaol for this treatment was 1.63 mg/g DW, which
was close to the experimental value (Table 2). Figure 1b
shows the response surface relationship between the 6shogaol content and the extraction temperature and
time. The obtained results were consistent with previous
a
studies, which reported that the 6-shogaol content increased with higher drying and extraction temperatures
and the lowest 6-shogaol content was achieved when the
freeze-dried ginger was extracted at a low temperature
(30 °C), whereas the highest 6-shogaol content was obtained when the ginger was dried and extracted at a high
temperature (80 °C) [17]. The results demonstrate that
the amount of 6-shogaol in rhizomes extract depends
more strongly on the extraction temperature than the
extraction time. Figure 2 shows UHPLC chromatograms
of ginger ethanol extract and standards.
Effects of extraction conditions on antioxidant activity
The DPPH stable free radical method is an easy, rapid,
and sensitive method for evaluation of free radical scavenging antioxidants. The results of the DPPH assay
showed that the antioxidant activity for all the extracts
was more than 62.5 % (Table 2). The DPPH activity was
particularly high for the extracts subjected to treatment
3 (80 °C, 4 h), with a value of 89 %. On the other hand,
the regression equation obtained using the antioxidant
activity (Y3) as the response variable was also significantly (P < 0.05) related to the variation of the independent variables. The coefficient of determination
(R2) obtained was 0.96 (Table 3). Significant (P < 0.05)
linear and quadratic effects of the extraction temperature and time on the antioxidant capacity were
b
Fig. 1 Response surface plot showing the relationship between the 6-gingerol (a) and 6-shogaol (b) content with the extraction temperature
and time
Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
Page 6 of 10
Fig. 2 (a) UHPLC full chromatogram of 6-gingerol standard solution (0.5 mg/ml) at tr = 11.509 min and 6-shogaol standard solution (0.4 mg/ml)
at tr = 19.940 min, (b) UHPLC full chromatogram of ethanol extract of Z.officinale Roscoe var. rubrum dried rhizome powder showing peak corresponding to 6-gingerol and 6-shogaol standard solution. Extraction condition: at 80 °C for 4 h
observed. The predicted model obtained for Y3 is
given below:
Y 3 ¼ 71:88 þ 9:22X 1 þ 2:78X 2 þ 4:63X 1 X 2
ð5Þ
The model F-value of 15.79 obtained for the antioxidant activity implies that the model is significant, and
the “Lack of Fit F -value” of 1.24 implies that the Lack
of Fit is not significant for the predicted model. Figure 3
shows the response surface plot for the relationship between the antioxidant activity (DPPH) and the extraction
temperature and time. An increase in the DPPH activity
was observed with increasing extraction temperature
and time. The increase in the DPPH activity may be due
Fig. 3 Response surface plot showing the effect of extraction temperature and time on antioxidant activity (DPPH) in Z.officinale var. rubrum Theilade
rhizome extracts
Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
to an increase in the 6-gingerol and 6-shogaol content in
the extract.
Correlation between 6-gingerol, 6-shogaol and DPPH
activity
Previous studies reported that the major bioactive
constituents of ginger are gingerols and shogaols with
high pharmacological activities [20, 21]. Herein, a significant (P < 0.01) correlation between the 6-gingerol and 6shogaol content and antioxidant capacity of the ginger
extract (R2 = 0.95 and 0.90) was observed (Fig. 4), which
is in agreement with observations by Ali et al. [22], who
reported that ginger extract with a high 6-gingerol and
6-shogaol content exhibited high free radical scavenging
activity. Recent study by Pawar et al. [23] and Guo et al.
[24] showed that there is an strong correlation between
antioxidant activity of ginger and 6-gingerol content.
Herein, 6-gingerol was also found to exhibit the most
potent antioxidant properties, whereas 6-shogaol was
the least potent. The results obtained in the current study
provide additional evidence to support the assumption
Page 7 of 10
that gingerols are responsible for the antioxidant activity
of ginger rhizome [25, 26]. The potent pharmaceutical
quality of 6-gingerol may be attributed to its chemical
structure. The predicted results were highly consistent
with the experimental results obtained using the optimum
extraction conditions predicted by the model, which validates the RSM model with good correlation.
Optimization of response
In order to obtain ginger extract with a high content of 6gingerol, 6-shogaol, and high antioxidant activity, the optimal reflux extraction conditions were determined based
on the combination of both responses. Multiple graphical
and numerical optimizations were carried out to determine the optimum level for the independent variables
with desirable response goals. One optimal condition was
obtained for all responses, which was reflux extraction at
76.9 °C for 3.4 h. Under the optimum conditions, the
corresponding predicted response values for 6-gingerol,
6-shogaol, and the antioxidant activity were 2.89 mg/g
DW, 1.85 mg/g DW, and 84.3 % respectively.
Fig. 4 Linear regression line between DPPH activity, 6-gingerol and 6-shogaol content in Z.officinale var. rubrum Theilade rhizome extracts
Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
Table 4 Verification of model for predicted optimum treatment
conditions (78.9 °C and 3.8 h)
6-gingerol
(mg/g
DW)
6-shogaol
(mg/g
DW)
Antioxidant
activity (%)
Predicted
2.89
1.85
84.3
Experimental
2.92
1.88
84.0
Verification of the model
An experiment was performed for verify the adequacy
of the developed extraction model, with the predicted
optimum treatment conditions (76.9 °C and 3.4 h). Under
this condition the obtained concentration for the 6gingerol and 6-shogaol content, and the antioxidant activity were 2.92 and 1.88 mg/g DW, and 84.0 %, respectively
(Table 4). The results of response surface analysis for the
6-gingerol and 6-shogaol content and antioxidant activity
were verified by comparing the predicted values (2.89 mg/
g DW, 1.85 mg/g DW, and 84.3 %) with the experimental
values (2.92, 1.88 mg/g DW, and 84.0 %). The obtained
results from verification experiment were in consent with
the predicted values, because not significant (P > 0.05)
Page 8 of 10
difference was observed between the verification experimental and the predicted values.
Evaluation of anticancer activity of optimized and
unoptimized ginger extract
Optimized and unoptimized extracts of Z.officinale var.
rubrum Theilade rhizome were used in order to evaluate
the anticancer activity against HeLa cancer cell lines.
Preliminary screening showed that rhizomes extracts
exhibited a significant anticancer activity against HeLa
cancer cells at concentration of 40 μg/mL with the inhibition rate of 51.8 and 62.3 % from unoptimized and optimized extracts, respectively (Fig. 5a). HeLa cells showed
71.7 % inhibition when treated with tamoxifen (positive
control) at the concentration of 40 μg/mL. Furthermore,
with optimizing of reflux extraction anticancer activity
of extracts were enhanced about 16.8 %. The half maximal inhibitory concentration (IC50) value of optimized
and unoptimized extract was found at concentration of
20.9 and 38.4 μg/mL respectively. The IC50 value for
tamoxifen was observed at concentration of 16.4 μg/mL.
As shown in Fig. 5b the normal cells treated with the
a
b
Fig. 5 Dose-dependent anticancer activity of Z.officinale var. rubrum Theilade rhizome extracts against HeLa cell line (a) and normal cell viability
(b). Tamoxifen was used as a positive control. Bars represent standard error of means
Ghasemzadeh et al. BMC Complementary and Alternative Medicine (2015) 15:258
optimized and unoptimized extract of Z.officinale var.
rubrum Theilade rhizome showed 70.13 and 69.43 % of
viability at concentration of 40 μg/mL, respectively. According to the obtained results, optimized and unoptimized
extracts showed non toxic effects at the concentrations
bellow 120 μg/mL. 6-gingerol and 6-shogale were reported
as a potent anticancer compound in ginger [27–30].
The results of previous studies showed that 6-shogaol
is able to kill fifty percent of Hela cancer cell line at concentration of 14.75 μM [31]. Then, it could be conducted
that enhancement of anticancer activity of optimized extract could be related to rising of 6-gingerol and 6-shogaol
content in extract.
4.
5.
6.
7.
8.
9.
Conclusion
Response surface methodology was successfully implemented for the optimization of the experimental conditions for achieving high 6-gingerol and 6-shogaol content
and antioxidant activity in ginger extracts. The results indicate that the extraction temperature and time affected the
extraction yields of 6-gingerol and 6-shogaol significantly,
and consequently the antioxidant activity of the extracts.
Reflux extraction at 76.9 °C for 3.4 h was determined to be
the most efficient condition for the extraction of 6gingerol and 6-shogaol from Z.officinale var. rubrum Theilade rhizome to provide high antioxidant activity. Optimized extract showed a more distinct scavenging activity
against the DPPH and also showed significant anticancer
activities toward HeLa cancer cell lines in a concentration
of 40 μg/mL without toxicity to normal cells.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
Study design and experimental work was by Ghasemzadeh. The first draft of
the paper was written by Ghasemzadeh and reviewed by Jaafar and Rahmat.
Rahmat participated in antioxidant and anticancer experiment. All authors
reviewed and approved the final version.
Acknowledgements
The authors would like to thank the Ministry of Higher Education Malaysia
and the Research Management Centre, Universiti Putra Malaysia (UPM) for
sponsoring this work.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Author details
1
Department of Crop Science, Faculty of Agriculture, Universiti Putra
Malaysia, 43400 Serdang, Selangor, Malaysia. 2Department of Nutrition &
Dietetics, Faculty of Medicine & Health Sciences, Universiti Putra Malaysia,
43400 Serdang, Selangor, Malaysia.
21.
22.
Received: 8 April 2015 Accepted: 11 June 2015
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